Igniting a carbonaceous stratum for in situ combustion



smcn m Sept. 10, 1968 F. A. KLEIN ET AL- IGNITING A CARBONACEQUS STRATUMFOR IN SZ 'IU IOMBUSTION Filed June 2:5, 1966 5 .1 6 uz om o l L w a x oI. 5 (1.21% 1 I 5 4 uzumomu: o a 1 4 636 a a J6 396 E03 w :o 9.6 wz a l0 2 w H mac 2580 D 110 1 m 2550: I 15. .1 5 p k N o w w wwmm.m

DILUENT AP! GRAVITY PRODUCTION OR IGNITION-AND PRODUCTION WELL INJECTIONWELL OIL STRATUM INVENTORS F. A. KLEIN M. R. DEAN PERMEABLE .LCERAMICLINER 'mxr RE CDQESEL on.

UTOIGNITABLE FUEL (TUNG on.)

FIG.

9 v ATTORNEYS United States Patent "ice '3,400,763 lGNlTlNG A--CARBONACEOUS STRATUM? FOR IN SlTU COMBUSTION" Frederick A. Klein and-Maurice R. Dean, llartlesullle, 0kla., assignors to v Phillips.Petroleum, Company,- a. corporation of Delaware Continuation-impart ofapplication. Ser. No. 523,408, Jan. 27, 1966. This application June 23,.1966, Sen.

6 Claims. (Cl. 16638) ABSTRACT'OF THE DISCLOSURE An annulus around awell. in an oil stratum is burned out to improve itspermeabilityandsubsequent oil. production by installing. a permeabletubular ceramic liner downhole,"injecting a slug of autoignitable fuel,such as tung oil, thru the. liner into the oil. stratum, injecting afollowing slug of liquid-Qhydrocarbon miscible with said fuel tofree theliner of said fuel. driving the aforesaid slugs deeper into the stratumwith injected inert gas. and thereafter injecting air thru the well intothe stratum to contact, ignite, and burnout the injected fuel andiii-place carbonaceous material.

This application is a continuation-in-part of ourcopending applicationS.N. 523,408, filed Jan. 27-, 1966, which isa continuation-in-part ofour copending application SN. 451,652,. filed Apr. 28, 1965 now.abandoned;-

This invention relates. to a process for igniting an oil.-

bearing subterranean stratum for propagating the resulting combustionzone thru. the stratum to produce oil therefrom, to an autoignitablefuel composition therefor, and to a method of opening upa stratumaround. a well to increased flow. I

The production of oil from an, oil-bearing stratum by in situ combustionis an accepted process in the petroleum industry. In order to, propagatea combustion zone thru a stratum, it is necessary to. ignite thein-place oil in a selected area of the stratum prior to the actualdriving step of the process. Common'techniques for igniting the oilin astratum comprise burning a fuel pack such as. oilsoaked charcoal in aweli penetrating the stratum, heating thestratum around the ignitionwell with a gas-fired healer or an electric heater, heating the stratumwith a thermitc starter, or with rocket fuels, etc. I

A more recent method is that disclosed in 11.5. Patent 2.683.510 (Dec.9. 1958) wherein a fuel spontaneously ignitable in contact with agaseous oxidant is burned in the ignition well by depositing the fueltherein and contacting same with the gaseous oxidant whereby the fuelignites and raises the temperature of the crude oil in the stratumadjacent the well to ignition temperature. Continued injection of airinto the ignited area moves the combustion zone thru the stratum towarda production well so as to produce oil therein.

In some in situ combustion operations, a. permeable ceramic linerisutilized in the ignition well which may thereafter become an injectionwell or a production well. Such a liner is disclosed and claimed in thecopending application of G. B. Heckler and R. F. Meldau, S.N. l0,- .149,filed Nov. 29!, 1965.. When utilizing a permeable 33430363 Patented,Sept. 10, 1958 ceramic liner of this nature andan antpignitable fuel,the liner absorbs fuel which insome instances is polymerizable in placeduring. subsequent heating, resulting in plugging of the ceramic linerand obstruction of the flow of fluids into and/or out of the stratum.

In all of the foregoing ignition methods, for heat to flow into thestratum adjacent the ignition well. at a desirably high rate, it isnecessary for the heat source to operate at a very high. temperature.In, some cases these.

high temperatures severely damage the formation around the ignitionwell. When the well casing extends thru the oil-bearing stratum, thecasing can also be severely dam-- aged. These high temperatures canveven damage. other parts of the well. -co rnpletion apparatus.

This invention is concerned with an autoignitable fuel' composition for,use in a methodor process for igmtutg anoil bearing stratum around anignition wellwithout overheating the wall of the wellbore and anydownhole equipment within the oil-bearing stratum or in burning outsolid to semi-solid carbonaceous deposits around a wellbore.

Accordingly, it is an object of the invention to provide anautoignitable fuel composition for igniting an oilbearing stratum aroundan ignition, well'which avoids overheating of the. wall of the wellbore.and equipment therein. Another object is to provide a method or processfor igniting an oil-bearing stratum around a well therein to establishin situ combustion in the stratum, which prevents overheating and damage.to the wall ofthe wellbore and equipment therein. A further object isto. provide a method ofinitiating in situ combustion in an oil-bearingstratum for propagating the resulting combustion zone thru the stratumbetween wells therein to produce oil thru one of said wells. Anotherobject is to prevent polymeriuition of certain'autoignitable fuels in aceramic liner in an ignition well when using such fuels. Otherobjects ofthe invention will become apparent to one skilled in the art uponconsideration of the accompanying disclosure.

A broad aspect of the process-of the invention comspontaneouslyignitablefuel and ignite same in an area of thestratum spaced from the wall ofthe-ignition well,

also. igniting the in-place crude oil. in this manner, the method orprocess develops a zone of elevated temperature within the oil-bearingstratum around the wellbore but spaced therefrom sutiiciently to providean insulating annulus between the hot combustion zone and the wall ofthe wellbore. This technique avoids overheating downhole equipment andallows the well to be completed for best sand control where sandproduction is a problem, as in unconsolidated oilsandsLikewise,overheating 'of the sand in the combustion zone is avoidedbecause of the relatively low ignition point of the spontaneouslyignitable fuel and the ignition of the native crude oil at its kindlingtemperature. This technique also assures that after the ignitiontemperature has been achieved there ward the offset well(s) (reverseburning front). The other procedure comprises injecting air thru thewell thru which the fuel was injected to establish a direct drive of thecombustion zone. It is to be understood that the term air isillustrative of other O -contai'ning, combustionsupporting gases.

In one embodiment of the invention, injection of a slug -of theautoignitable fuel is followed by injection of a second slug of ahydrocarbon oil of substantially higher ignition point than the fuel todrive the autoignitable fuel into the stratum away from the wall of theignition "well.

The liquid hydrocarbon thus injected should be miscible with the fuel soas to flush the fuel from a narrow annulus of the stratum adjacent thewellbore. In the event a ceramic liner is utilized in the ignition well,this feature of the invention is particularly advantageous in freeingthe porous liner of autoignitable fuel, thereby decreasing the heatingwithin the ignition borehole and preventing polymerization of the fuelin the liner (in the event the fuel is polymerizable).

v Hydrocarbon oils suitable for use as the second slug include liquidhydrocarbons ranging from gasoline to light crude oil and includingdiesel oil, kerosene, gas oi1, etc. The liquid hydrocarbon to beinjected following the fuel slug should be miscible with the fuel andhave an A.S.T.M. final boiling point less than 700 F. with a carbonresidue less than 1.0 percent by weight. After injection of the slug ofliquid hydrocarbon thru the ignition well into the surrounding stratum,it is preferable to inject a slug of nonoxidizing gas to drive the fueland liquid hydrocarbon into the stratum away from the ignition well ashort distance, such as one foot to several feet. However, this step maybe omitted and oxidant, such as air or other O containing,combustion-supporting gas, may be injected directly behind the slug ofhydrocarbon liquid which is not autoignitable. This assures ignition ofthe autoignitable fuel in an annulus spaced from the ignition well.

'After ignition of the autoignitable fuel, the injection of oxidant(air) is continued so as to move a combustion zone away from thewellbore toward one or more ofi'set wells to become production wells. Itis also feasible to either reverse the How of air after ignition, orinject air thru the offset well( s) so as to move the resultingcombustion front toward the offset well(s) countercurrently to the howof air thru the stratum.

Another embodiment of the invention comprises forming an intimatemixture of the autoignitable fuel, the higher ignition point hydrocarbonfuel and an oxidation catalyst and injecting the mixture into the areaof the stratum to be ignited. Thereafter, the fuel composition is thencontacted with injected (air) to ignite same,

The autoignitable fuel composition of the invention consists essentiallyof an intimate mixture of 1) an autoignitable fuel of the group tungoil, linseed oil (boiled or raw), red oil, castor oil, turpentine, talloil, tall oil fatty acids, oleic acid, and linseed oil fatty acids andmixtures thereof in an amount in the range of 35 to 95 weight per centof the composition, (2) a liquid oxidation catalyst or accelerator in aconcentration in the range of 0.025 to 1.0 weight percent of the fuel of(l), and (3) a liquid hydrocarbon fuel having an ignition temperaturesubstantially above the ignition temperature of the fuel of (1). saidhydrocarbon fuel ranging from gasoline to heavy crude oil; The amount ofthe autoignitable fuel of 1) required increases with the lighterhydrocarbon fuels of (3), at least about 35 weight percent beingsufficient with crude oils and at least 75 weight percent being requiredwith gasoline.

Another embodiment of the invention comprises burning out an annulus ofcarbonaceous stratum around either an injection or a production well toincrease the permeability thereof and open up same to permit fasterinjection and production rates. The autoignitable fuel or fuelcomposition is deposited in an annulus of about t to 5 feet or more inradius immediately surrounding the well and burning thereof is effectedby contact with injected 0: and injection is continued to burn out thefuel and carbonaceous deposit, thereby greatly increasing thepermeability of the annulus. The-termination of 0, injection thenextinguishes the fire and injection of fluids there thru or theproduction of fluid hydrocarbons can be effected at faster rates. Thisaspect of the invention is excellent for well stimulation to increaseproduction.

It has been demonstrated that 33 standard cubic feet of air per pound oftung oil in place in a sand. is required to burnthe tung oil. An Ottawasand pack 26 inches long in a 2-inch combustion tube was saturated withtung oil. Air at 500 p.s.i. pressure was passed'thru the tube at a fluxof 150 s.c.-f./hr.-ft. and the tung oil was ignited and consumed.

Another test was made to determine if tung oil, when admixed withreservoir oil, is subject to autoignition. This test was performed in anisothermal 2-inch.Pyrex combustion tube using an Ottawa sand packcontaining 9 weight percent of a mixture of percent catalyzed tung oiland 25 percent Morichal Group I crude oil (cobalt naphthenate catalyst).Air was injected into the tube at an air flux of 50 s.c.f./hr.--ft. andthe temperature reached 400 F. in 2.3 hours, the initial temperaturebeing 140 F., simulating reservoir conditions. The pressure was 500p.s.i. This test demonstrates the feasibility ofutilizing a mixture ofautoignitable fuel and crude oil as a fuel in the instant process. Italso demonstrates that an autoignitable fuel, when admixed with in-placecrude oil, will stiii onction in the manner required.

In operation of the process, the injected slug of spontaneouslyignitable fuel is driven into the stratum so that the leading edgethereof is at least one foot, preferably several feet, and up to 50 feetfrom the wall of the wellbore before contacting with the gaseousoxidant. In one embodiment of the invention, a non-oxidizing gas isinjected thru the ignition well subsequent to the injection of thereadily oxidizable fuel so as to drive the fuel into the stratum remotefrom the wellbore and render the stratum gas permeable. Anynon-oxidizing gas such as oil field gas (natural gas), light gaseoushydrocarbons, combustion gas, nitrogen, etc., may be used for thispurpose but oil field gas is preferred because of its ready availabilityand low cost.

In igniting an oil-bearing stratum containing a crude oil of highkindling or ignition point such as one of about 375' or 400 F.,' it ispreferred to injectin admixture with the spontaneously combustible fuela second'fuei having a kindling or ignition point substantiallylower-than the ignition point of the native'crude oil but substantiallyhigher than theignition point of the spontaneously combustible fuel. Theless readily oxidizable fuel is incorporated in the injected slug in aconcentration in the range of about 1 to 50 volume percent, the readilyoxidizable fuel being in the range of 99 to 50 volume percent oftheinjected slug. The second fuel of higher ignition temperature comprisesany liquid hydrocarbon material having an ignition temperature underambient conditions in the range of about 275-350 F. Such fuels askerosene, distillate, cycle oil, and some crude oils have ignitionpoints" the oil in place. it also helps'to adjust theigniti'ontemperature of all-of'the combustible material in' the'slugthru' mixing.

The spontaneously ignitable' component of-the' iniected Gil slug isseiected'from any ofthe well known-*materiais which ignite spontaneouslyunder oxidative conditions at the temperature prevailingin the-stratumwhich 5510 treated. Such materials inc'lude'unsaturated compounds liketurpentine, linseed oil, tall-oil, tung'oil, red-oil; etc.

Generally, the oxidizableliquids disclosed in"U.S." Patent 2,863,510.excepting-the aminecompounds, are; operablein the process.Hypergolic-fuelsgenerally'are-withirfithe".

scope of the invention."

Suitable gaseous oxidants-include air,-'oxygen,-oxygen-" enriched air,ozone, gaseous-nitrogen oxides, and m'ixtures of thesegases.when'utilizing airwithout--th'e 0,-

enrichment and without an oxidation-catalyst; the'=ptes'-= sure requiredfor spontaneous ignition-is usually=atleast edge of the fuel slug. The'O-containi'ng gas must'have an oxygen partial pressureof at least 6 lbs.whether atmospheric air or 'oxygen-enriched'air is utilized.

It has been found 'that-incorporationbf an oxidation" catalyst in minorconcentration'in'the injected fuel slug facilitates spontaneousignitiori' ofthe fuel and: makes-it feasible to ignite the'fuel slug'withordinary' air at atmospheric pressure. It is preferred to utilizethe catalyst in liquid form so as to avoidpluggin'g the-stratum: A'preferred catalyst is cob'altnaphthenate, which is readily soluble insuch fuels as thosenamed'abovm. Other catalysts include oilsoluble saltsand other compounds-of the metals listed as oxidationcatalyst's in-Berk'hianet' aL,

Catalysis, Reinhold Publishing Corp..- 330 W: 42nd St'., NewYork';N.Y'., 1940; pages'797-809:

While theignition-step can be effected in: the: stratum in thepresence'of connate 'water; it is preferred tol'air 'dry the stratumprior to the injection ofthe fuePsIug' When any substantialamount ofconnate"- water is'presentJ-In 'the presence of small concentrations ofcon'nat'e' water the heating produced bythe spontaneous ignition of' thefuel slug increases the temperaturein-the'contacting zone'until theboiling: point of w'ater' is'-' reached under arn'biem'comditions andthe water this heatingzone is-vaporizecl until the ignitionzone'is'relatively dry. Theri'the-tempera' ture produced by thespontaneous" heating of the fuel' in contact with oxygenrises until theignition point is reached and igniti'oii' is'actually' initiated so asto produce a burning zone. Drying-our of the stratum intermediate. theignition and surrounding injection wellsis readily accomplished bydriving air or other drying: gas thru' the stratum between the wells.Following the step of dry- "mg-out with an oxidizing gas, such as air,an'inertgas'is injected to displace the'air fromthe section of stratuminto which the autoignitable fuel is to be injected;

v The following examples demonstrate the invention but are not to beconstrued as unnecessarily limitingsamer Example I Runs were made withseveral spontaneously ignita'ble fuels under'controlled' conditionsin a2" diameter Pyrex tube containinga 2-" long section of sand and liquidfuel in a sand to fuel ratio' of 9:1; In all cases, the contained" packwas preheated to'150 F. while flushing with nitrogen. In runs' 1-13,inclusive, oxygen was passed intonthe tube at a rate of s-.c.f./h'r.-ft.at atmospheric pressure.

In runs 14' and air was passed into the tube at a rate of s.c.f./hr.-ft.at atmospheric pressure. The rise in.

temperature within the" tube was balanced by extemalh.

f t 'u TA BLE Spontaneous- Ruu i ()xidlznhlo material 1 1 ignitiontcmp.. F.

l.'... lurthnilml linseed oil; 150 I 2. 75% i. ll. linseed oil. Murinlml(in. ii crude.- 200 3 1. ll. linseed oil. Mnriehul-tlp ll enido; 265 4ill-hydrated castor oil 1X5 5 Tununil 155 6 lat acids. 150

Tull nil fatty acids; 8. Rr-d oil (olnic acid)- 204 0.. Crude tnlioil200 I 10 ruditall'nll l',,. catalyst l 174 ll llt-tlolH-ifl caialyslL... IN) I 12 Tall oil fatty twi l+1% catalyst 1.50 13 Tall oil fattyaeirl+0.5,7. catalyst l H l"; B: linseed oiH- catalyst- 150 15'. Talloil fatty ucltl+cntyalst 3 15) Catalyst: solution was leadnaphthenate-+oobalthaphtheuate (9:1). 1 Catalyst solution was cobalt.naphthenate (0.! wt. prcceut. cobalt).

Example ll- Similar tests to'those'of' Example I were run with MorichaiGroupIiand- Morichalffiroup II crude oil in the sand: The crude oil wasadmixed with cobalt naph-' thenate-sin' a concentration of 0.1 percentcobalt. The

sandtemperature was raised to 150 F. and 0 at a flow rate of'5' s.:.f.'/hr.-ft; was passed into the'packed sand in'the/ combustion tube.and therewas no autoignition of spontaneouslyignitable' fuel withconcentration. of catalyst varying from 0.025 to 0.1 weight-percent andautoignition' was readily achieved at a starting-temperature of 150 F. vIgniting: the' spontaneouslycombustible fuel disclosed herein with'airas an' oxidant isaided by increasing the pressuresubstantiallyabove-atmospheric pressure. Using O enriched. aircontaining: at least"40% O, enhancesautoignition.

Example 111' In anotherrun using pure'O instead of air, the packin'the'combustion-tubeof=Example I hada water saturationof" 16% ofthe-=pore-volume and: an autoignitable oil 1 saturation-=of 50% ofthe"pore .volume, using tall oil fatty acid and cobalt'inaphthenate in a.concentration of 0.1 weight PCX'CBHFCO'JZJE. In this run'. thetemperature rose slowly until thewater inthe sand was evaporated andthen much-more rapidly asignition= took place. The ignitionwasterminatedat 440 F. while the temperature was risin'g=att.6 F.:perminute. i

Example In testing" the mechanics" of the spontaneous ignitionprocedure, an 18-inch long; Fla-inch diameter stainless steel tube wasused. it .waspacked with 9.2-inch section of Ottawasand mixed withautoignitable oil (pius cobalt naphthenate) sandwiched between twosections of Ottawa sandcontaining Group '11 Morichal'oil. Counterflowcomb'ustiorr was initiated in the autoignitable section by subiecti'ngit to the flowof oxygen at aflux of 10 s.c.f./hr.-

ing 0.1 weight percent cobalt as cobalt naphthenate as catalyst. Thisoil mix. was present at a concentration of 17-10 BPAF and the flankingsections contained 1350 BPAF of Morichal Group-II oil.

The total pack was heated to 150 F. (the reservoir temperature of theGroup II Morichal sands), while it was fiushed'with nitrogen. The lossof the spontaneously generated heat when oxygen wasiniected wasprevented by maintaining the temperature of the outside of the tubesubstantially equal to that of the interior with an electric heatenAperiod of 6.5 hours was required tobring the temperature of the sand to800 F..by spontaneous heating. During this time, the combustion frontmovedfrom 7 I the middle section containing the autoignitable oil mixinto the upstream section containing Group II oil.

The above test with Morichal oil clearly demonstrates that in-placecrude oil is readily ignitable by the process of the invention and thata combustion zone can be moved thru an oil sand countercurrently to theflow of oxygencontaining, combustion-supporting gas.

Example V ofN- and air was then substituted for N, at a pressure of 500p.s.i.g. There was immediate sustained reaction at a 140 F. and thetemperature of the pack rose from 140 to 201 F. in 130 minutes.Thereafter, the rate of temperature rise increased substantially, risingto 398 F. in 30 minutes. The run was terminated when the pack reached398 F. at which time the temperature was increasing at the rate of 4 F.per minute.

A more complete understanding of the invention may be had by referenceto the schematic drawing of which FIGURE'l is an elevation inpartialcross section thru an oil stratum penetrated by an ignition welland an offset well and FIGURE 2 is a graph showing the relationshipbetween API gravity of the hydrocarbon fuel and the minimumautoignitable oil required.

Referring to FIGURE 1 of the drawing, an oil stratum 10 is penetrated byan ignition well 12 and an offset well 14. Well 12 is provided with aperforate injection tubing 16 and a permeable surrounding ceramic liner18, tubing 16 being imperforate above the liner 18 and the liner l8terminating substantially at the upper level of the oil stratum. Well-14 is provided with a tubing string 20 extending thru the wellhead. I

In the stage of the process illustrated'in the drawing, a slug ofautoignitable fuel, such as tung oil 22, has been injected thru tubing16, liner l8, and into the stratum. A second slug of liquid hydrocarbonsuch as diesel oil 24 has been injected in the same manner behind theslug of 1 fuel, forming a mixture 26 of the fuel and diesel oiladjacent' the interface of the slugs. At the stage of operationillustrated, the next step in the process comprises either injecting anoxidant such as air or a non-oxidizing gas such as nitrogen, combustiongas, etc., followed by oxi dant injection.

It is also feasible to inject a non-oxidizing, nondeleterious gas thruwell 12 to drive the fuel and liquid hydrocarbon deeper into the stratumand then inject air or other oxidant continuously thru tubing string 20of well 14 so as to initiate ignition at the leading edge of fuel slug22 and cause the resulting combustion zone to move thru the stratumtoward well 14 with production passing thru well 12 and out tubingstring 16, which passes thru the wellhead. Such gases include CO fluegas,

, N etc.

' reservoirs of substantial depth temperatures are at this level andupwards so that autoignition of such a fuel is readily effected byinjecting air, particularly at the pres-- sures required for suchinjection.

To illustrate with FIGURE 2, Moric'nal Group II crude oil has an APIgravity of 8 and requires at least 35 wt.

percent tung oil mixed therewith and with catalyst to provide anautoignitable fuel composition at the minimum temperature of about 150F. Naphtha requires a minimum of wt. percent and gasoline, a minimum ofwt. percent..0f course, higher concentrations of tung oil up to wt.percent of the composition are operable and provide suflicient addedfuel to be effective in igniting the native oil or carbonaceousmaterial. Increasing the air injection pressure lowers the ignitionpoint of the fuel composition in the presence of catalyst.

When combining a high viscosity crude or tar with tung oil, it improvesthe handling characteristics of the composition to incorporate thereinat least 5 and up to 15 wt. percent of a low viscosity hydrocarbon fuelhaving a considerably higher API gravity. Thus, when using a crude of 8API gravity admixed with tung oil, the viscosity of the composition isso high that it is desirable to blend therewith a hydrocarbon fuelranging from a heavy gas oil to gasoline to lower the viscosity of thecomposition. The required concentration of tung oil increases as thegravity rises. Other autoignitable fuels behave simiing in situcombustion process wherein air is fed thru an offset injection well andforced to the combustion zone to propagate same thru the stratum to theinjection well(s). Any suitable well pattern may be utilized in thisoperation. It is also feasible to ignite the stratum by the method ofthe invention in a section of the stratum spaced from the ignition wellby injecting the oxidant thru an offset well and subsequentlyterminating injection thru the offset well and injecting air thru theignition well so as to propagate the combustion zone to the originalinjection well by direct drive.

Certain modifications of-the invention will become apparent to thoseskilled in the art and the illustrative details disclosed are not to beconstrued as imposing unnecessary limitations on the invention.

We claim: j

1. A process for igniting and burning carbonaceous material in arestricted section of oil stratum adjacent but spaced from an ignitionwell therein in which a perme-. able ceramic tubular liner is positionedin said well downhole within said stratum, which comprises the stepsof:.

(l) injecting into said stratum thru said ignition well a slug of anautoignitable fuel (when contacted with O in an amount sufficient toimpregnate a substantial but limited section of the surrounding stratum;

(2) injecting a liquid hydrocarbon miscible with the fuel of step (1)through said well and thru said ceramic liner to remove substantiallyallof said fuel from said liner, prevent formation of plugging material insaid liner when oxidant of step (3) is injected therethru, and move saidfuel out of a narrow section contiguous to said well; 7

(3) subsequent to step (2) injecting a gaseous oxidant providingsufficient 0, concentration to cause autoignition of the fuel of step(1) into said stratum thru said well and said liner into contact withsaid fuel so as to effect ignition thereof in said restricted scction;and i v (4) continuing the injection of oxidant of step (3) so 2. Theprocess of claim 1 wherein said fuel includes an oxidation catalyst andsaid gaseous oxidant consists essentially of air.

3. The process of claim 2 wherein said liquid hydrocarbon in step (2)consists principally of diesel oil. I

4. The process of claim vl wherein the oil in said stratum has anignition point of at least 375 F. and a liquid hydrocarbon materialhaving an ignition point in the range of 275m 350 F. is incorporated inthe fuel of step (1) in a concentration in the range of l to 50 volumepercent of the resulting fuel.

5. The process of claim 1 wherein a substantial slug of an inert gas isinjected into said stratum thru said 9 well and said liner intermediatesteps (2) and (3) to displace fuel of step (1) and liquid hydrocarbon ofstep (2) radially into said stratum away from said well.

6. The process of claim 1 wherein the autoignitable fuel of step. (1) isselected from the group consisting of tung oil, linseed oil, tall oil,red oil, castor oil, .oleic acii linseed oil fatty acids, tall oil fattyacids, turpentine, and

References Cited UNITED STATES PATENTS Tadema et al 166 -38 Parker'16611 XR Wyllie 166-25 Cline et al. 166-418 Bednarski et al. 166-38 XRPrats 15611 3 10 STEPHEN J. NOVOSAD, Primary Examiner.

